There are several patents which disclose alpha-olefin polymerization catalysts being treated with halogen-containing organic compounds. The practice of most of these patents involves the direct milling of the solid titanium-containing catalyst component with a halogen-containing organic compound during the course of a complex catalyst preparation procedure. These techniques suffer from reproducibility problems and usually result in a catalyst of low activity.
A few of these patents show that certain halogen-containing compounds can be added before, during or after the polymerization process. For example, U.S. Pat. Nos. 3,957,910, 3,349,064, 3,326,872, 3,072,630, 3,692,712 and 3,462,399 each disclose the addition of halogen compounds to Ziegler-type catalysts. However, all of these processes are disadvantageous for various different reasons.
Among the advantages that the practice of the instant invention offers over the art cited above includes (1) the elimination of a step in the catalyst preparation; (2) increased catalyst activity; (3) increased polymer yield; and (4) an increase in the polymer fraction which is insoluble in hot n-heptane. Furthermore, this invention has the advantage of being applicable to commercially available pre-prepared catalysts. Thus, the product output from the existing polypropylene plants using conventional commercial catalysts can be increased without significant capital expenditures by the use of this invention.